The instant invention relates to hoisting devices and jacks, in particular hoisting devices of a compact nature comprised of a plurality of interconnected pivoting links.
There is a need in many industrial and service arts for a jack or hoisting device which would exhibit compact dimensions, large vertical travel, and a substantially vertical and uniform-velocity travel path for the lifted object or device. Such needs are commonly associated with floor jacks employed in automotive repair shops, with elevating camera dollies in film-making and television production, with lifting devices used by heating and ventillating contractors, in mobile materials handling hoists, and many others.
Several solutions proposed in the prior art utilize pivoting links, especially the widely employed mobil form of the scissors type work platform--and its many analogues in other fields--in which load-lifting links are pivoted in a base and caused to rise by means of a hydraulic actuator, or a manual or electric screw jack. Thus, the crossed link connections of some prior art lifts require twice the lateral space of a comparable lift using only one side of the crossed arm concept to achieve the same displacement. Displacement of the crossed link lift requires at least one set (or side) of the link arms to displace along a bearing surface, thus creating design problems and undesired friction.
It is, therefore, a primary object of the invention to teach the construction of compact hoisting devices employing at least a pair of hoist links--one pivoted in a base, the other pivoted on a cross-shaft at the outboard end of the one--which coact in such a manner that the path of a load support attached to the outboard end of the second hoist link is substantially vertical.
It is a further object of the invention to describe the construction of transmission means governing the relative angular movement of the hoist links in such a hoisting device, so as to generate the desired, substantially vertical travel path, and to ensure that a load platform attached to the end of uppermost hoist link retains a constant alignment.
It is yet another object of the invention to teach the construction of multi-linked hoists, for generating large vertical travel ranges.
It is a further, particular object of the invention to provide a compact elevating device for television and motion picture cameras wherein the substantially vertical travel path of the camera mount is combined with minimal motion around all other degrees of freedom.